The present invention is generally directed to a telecommunication network and, more particularly, to a fixed cellular communications system that incorporates the use of a private branch exchange (PBX) or key system.
The use of telecommunication networks for business and personal purposes is typically regarded as a necessity of modern living. Use of these networks has increased exponentially over the past few decades. Today, telecommunication networks include, among other things, two major types of conventional telephone systems.
The first of these two conventional telephone systems shall be referred to herein as a landline telephone system. Landline telephone systems are the conventional wire-based systems that are found in most homes or businesses. Because these systems are wirebased, to develop such systems, the telephone service provider must acquire rights of way and establish a network infrastructure, which are costly endeavors. These telephone systems are typically regarded as being fixed in that the mobility of a telephone set connected to the system is limited to a relatively short range.
The second of these two conventional telephone systems shall be referred to herein as a cellular telephone system. Cellular telephone systems are the conventional wireless systems that have become increasingly popular among telephone service subscribers. The primary advantage of using these systems is that they permit mobility of the telephone handset, which allows the user to be reached even when he is located away from the home or office. The telephone handsets for cellular telephone systems are typically either connected to a cellular transceiver unit mounted in the trunk of an automobile or are portable, hand-held units that include a cellular transceiver in a common housing and can travel with a subscriber in his or her pocket or bag.
While the popularity of cellular telephone systems has increased, the expense associated with the use of such systems has steadily decreased, particularly when taking into account the standard rate of inflation. The use of cellular systems, however, is still generally more expensive than the use of conventional landline telephone systems. Cellular service providers, which often are not associated and/or affiliated with landline service providers, could establish and market billing plans that provide incentives for telephone subscribers to place mobile-to-mobile (cellular-to-cellular) telephone calls as opposed to mobile-to-landline and/or landline-to-mobile telephone calls. In many cases, the cost for a cellular-to-cellular call is priced at only about twenty-five percent (25%) of the cost for a similar cellular-to-landline call. The cost of mobile-to-mobile calls is less expensive because it is unnecessary to route such calls through the central office of a landline telephone service provider. Accordingly, the landline service provider does not charge the cellular service provider a service fee for utilizing its central office. To the contrary, mobile-to-landline and/or landline-to-mobile telephone calls are routed through the central office of a landline service provider, which charges a service fee for utilization of its central office. That fee is ultimately passed through and billed to the cellular telephone service subscriber.
In today""s marketplace, many firms conduct business by having some employees at a main office and having other employees in motor vehicles out in the field who travel from work site to work site. For present purposes, those employees out in the field will be referred to as xe2x80x9cmobile employeesxe2x80x9d and those employees in the main office will be referred to as xe2x80x9cfixed employeesxe2x80x9d.
One example of such a firm is a cable television company. Typically, cable television companies employ servicemen or technicians who drive to a job site, perform a service (such as installation or repair of cable television service at that site) and then drive to the next job site. These servicemen are mobile employees.
In other examples, some firms have employees who continually roam. For instance, with respect to a taxi cab service company, drivers (mobile employees) travel from location to location in order to transport passengers, while dispatchers (fixed employees) remain at the firm""s main office and communicate with the drivers. The drivers do not actually stop at a work site to perform a job. Rather, they pick up passengers and transport them to a requested site. It will be appreciated that these examples are nowhere near exhaustive of the firms that have both mobile and fixed employees. It will further be appreciated that in the vast majority of these firms the mobile employees contact fixed employees working at the main office several times during each working day, and vice versa.
In these firms, it is impractical for the mobile employees to stop what they are doing each and every time they desire to place a telephone call to a fixed employee at the firm""s office. In particular, for each time a mobile employee is required to contact a fixed employee at the firm""s office, it would take too long and be too disruptive for the mobile employee to drive his/her motor vehicle off the road, park the vehicle, exit from its passenger compartment, approach a coin-actuated telephone, insert the appropriate currency, and dial the office telephone number. Further, it is beneficial if the mobile employees can be reached easily at any time. Accordingly, use of a wireless form of communication by mobile employees provides significant benefits, some of which are noted above. A cellular telephone with transceiver is typically the most practical and desirable form of communication.
Given the billing plans offered by many cellular telephone providers, where cellular-to-cellular calls can be completed for a cost substantially less than the cost of similar cellular-to-landline calls, if a firm""s mobile employees use cellular transceivers to place outgoing and receive incoming telephone calls, it makes sense for the fixed employees to communicate with the mobile employees by using cellular transceivers as well. In that way, the firm""s overhead and operating costs can be reduced.
In prior art telephone systems, it is known to use a fixed cellular communications system to provide for mobile-to-mobile calls. An example of a fixed cellular communications system can be found in U.S. Pat. No. 4,922,517, issued to West, Jr. et al., the disclosure of which is hereby incorporated herein by reference. Fixed cellular communications systems typically incorporate an interface unit that encodes signals received from a landline telephone unit and decodes signals received from a remote cellular telephone unit. These interface units typically include, among other possible things, a cellular transceiver, logic circuitry and a power supply. The interface unit, when combined with the landline telephone unit, permits the landline telephone unit to function as if it were a cellular telephone unit. Under such circumstances, outgoing calls transmitted to a remote cellular telephone unit and incoming calls received from a remote cellular telephone unit are made on a mobile-to-mobile basis.
In light of these prior art fixed cellular communication systems, business firms could incorporate a landline telephone unit and an interface unit for every fixed employee so that calls made to and received from the mobile employees would be made on a mobile 10 to-mobile basis and the firm could take advantage of any applicable cost effective billing plans. Use of an external telephone line for every fixed employee, however, is impractical, especially for those business firms that have a relatively large number of fixed employees.
It will be appreciated that business firms often employ a private branch exchange (PBX) and/or a key system unit (KSU) for their telephone service. These systems allow for the switching of calls between the fixed employees on local lines, while simultaneously allowing the fixed employees to share external lines (known as trunk lines). The primary purpose of these systems is to save the additional cost that would otherwise be associated with requiring an outside telephone line for each fixed employee. For purposes herein, the words xe2x80x9cprivate branch exchangexe2x80x9d and/or the initials xe2x80x9cPBXxe2x80x9d shall be interpreted to mean both a private branch exchange and a key system unit. Accordingly, those words and/or initials, when used in the appended claims, shall cover both types of systems literally.
Those business firms that use a PBX or KSU for their telephone service could try to employ the interface units of the prior art in those systems to establish a fixed cellular communications system. What those firms would discover, however, is that using the prior art interface units with PBX and/or KSU systems creates several unforeseen problems. Among other things, no call teardown occurs when calls are terminated by the remote cellular telephone unit. As such, the prior art interface units have not, until now, been designed to function properly when used in association with a PBX and/or KSU.
As is well known in the art, in cellular telephone systems, upon completion of a mobile-to-mobile call between two cellular telephones whose users subscribe to cellular service offered by the sane cellular service provider, one unit terminates the call by transmitting an appropriate end of call (EOC) signal to the mobile telephone switching office (MTSO) utilized by the cellular telephone service provider. The MTSO receives the EOC signal from that unit and either relays that end of call (EOC) signal to the other cellular unit or generates another end of call (EOC) signal for transmission to the other cellular unit. With respect to fixed cellular communications systems, the cellular transceiver included as part of the interface unit either receives an EOC signal (when the call is terminated at the remote unit) or, alternatively, transmits an EOC signal (when the call is terminated at the landline telephone unit associated with the interface unit).
When the call is terminated at the remote unit, which is often the case, the prior art interface units typically do not cooperate with the functionality of PBX and/or KSU systems. In particular, when the cellular transceiver included as part of the interface unit receives an EOC signal from the MTSO, it responds by powering down. Nothing else notable occurs. As a result, the trunk line used for the call within the PBX and/or KSU system remains activated. From the standpoint of the PBX and/or KSU system, the call is never terminated, and the trunk line is never released, thereby rendering it useless.
In light of the foregoing, it is desirable to design a fixed cellular communications system for use with a trunk line of a private branch exchange and/or key system unit.
It is also desirable to design a fixed cellular communications system that effectuates call teardown when used in association with a trunk line of a private branch exchange and/or key system unit.
It is further desirable to design an interface unit for a fixed cellular communications system, wherein the interface unit causes its associated trunk line to be released upon termination of a telephone call at a remote telephone unit.
It is yet further desirable to design a fixed cellular communications system that includes call disconnection supervision control circuitry for use in association with a trunk line of a private branch exchange and/or key system unit.
It is still further desirable to design such a system that includes call disconnection supervision control circuitry that monitors a physical quantity attributable to its associated cellular transceiver and responds to a transition in the value of that physical quantity by causing its electrically coupled trunk line to be released.
These and other objects of the preferred form of the invention will become apparent from the following description. It will be understood, however, that an apparatus could appropriate the invention claimed herein without accomplishing each and every one of these objects, including those gleaned from the following description. The appended claims, not the objects, define the subject matter of this invention. Any and all objects are derived from the preferred form of the invention, not the invention in general.
The present invention is directed to a cellular interface unit for use in association with a trunk line of a private branch exchange or a key system unit. The cellular interface unit includes a cellular-type transceiver, a power supply and control circuitry. The cellular-type transceiver is used for mobile-to-mobile telephone calls with remote cellular telephone units and for mobile-to-landline telephone calls with remote landline telephone units. The control circuitry is used to convert signals between the cellular transceiver and the private branch exchange or key system unit so that the transceiver and its interconnected PBX or KSU function appropriately and so that use of the trunk line establishes a cellular telephone call, while resembling a landline telephone call through the PBX or KSU. Included within the control circuitry is call disconnection supervision circuitry that is responsive to the receipt of an end of call signal from the mobile telephone switching office. In response to the receipt of such signal, the call disconnection supervision circuitry causes the private branch exchange or key system unit to deactivate its associated trunk line and tear down the telephone call by monitoring a physical quantity attributable to the transceiver associated with the interface unit and responding to a change in that physical quantity. The power supply provides a source of electrical energy for the cellular transceiver and the control circuitry.